1. Field of the Invention
The present invention relates to a crystal oscillator for surface mounting, and more particularly to a surface-mounted crystal oscillator and a manufacturing method thereof that can improve productivity and miniaturization.
2. Description of the Related Art
[Prior Art]
Since a surface-mounted crystal oscillator has a small size and light weight, it is particularly built into a portable type electronic device as a frequency or time reference source.
As conventional surface-mounted crystal oscillators, there is one which has a crystal piece mounted on a ceramic substrate and has a concave cover put upside down to effect airtight sealing. In recent years, a frequency deviation Δf/f is relatively moderate, and there is an inexpensive consumer surface-mounted crystal oscillator of, e.g., ±150 to ±250 ppm.
In particular, a general configuration of a conventional surface-mounted crystal oscillator is that a pattern of a metal electrode of, e.g., AgPd (silver.palladium) is formed on a ceramic substrate, a support electrode of AgPd is laminated on a portion that supports a crystal piece, and the crystal piece is lifted by this support electrode.
That is because oscillation is obstructed and an equivalent resistance value is deteriorated when a central portion of the crystal piece comes into contact with a surface of the ceramic substrate (a base), and hence the support electrode on which the crystal piece is mounted must be raised from a base surface to some extent.
It is to be noted that the metal electrode and the support electrode are made of AgPd because this substance is hardly oxidized.
[Related Art]
In addition, as related arts, there are Japanese Patent Publication No. 2007-158419 “Surface-mounted Crystal Oscillator” (Nihon Dempa Kogyo Co., Ltd.) [Patent Document 1], Japanese Patent Publication No. 2003-179456 “Crystal Product Surface-mounted Container and Crystal Product Using This” (Nihon Dempa Kogyo Co., Ltd.) [Patent Document 2], and Japanese Patent Publication No. 2001-110925 “Conductive Cap, Electronic Component, and Insulating Coating Forming Method of Conductive Cap” (Murata Manufacturing Co., Ltd.) [Patent Document 3].
Patent Document 1 discloses a configuration that a crystal piece 3 is mounted on an IC chip 2, the IC chip 2 and others are formed on a mount board 4, and a metal cover 5 is provided in a surface-mounted crystal oscillator.
Further, Patent Document 2 discloses a configuration that a crystal piece 3 is provided on a single-layer substrate 1A through a crystal terminal 6 and airtightly sealed by a cover 2 in a crystal product surface-mounted crystal oscillator.
Furthermore, Patent Document 3 discloses that an insulating film 55 having a rectangular frame shape is formed on a substrate 51 at a portion where a lower opening end surface of a metal cap 52 is in contact with an upper surface 51a of the substrate 51 in [0005] of Prior Art.    Patent Document 1: Japanese Patent Publication No. 2007-158419    Patent Document 2: Japanese Patent Publication No. 2003-179456    Patent Document 3: Japanese Patent Publication No. 2001-110925
However, in a conventional surface-mounted crystal oscillator, although the metal electrode and the support electrode are made of AgPd because this material is hardly oxidized, since the support electrode requires a thickness to keep the crystal piece away from the base surface, AgPd is applied, e.g., three times by screen printing and laminated for the support electrode, and hence there is a problem that manufacture of the surface-mounted crystal oscillator is complicated.
Since AgPd has low viscosity in particular, a thick film cannot be formed at a time, and hence a process of forming a thin film and laminating the thin film is required.
Moreover, since AgPd has low viscosity, the support electrode is formed on the metal electrode, but an AgPd film of the support electrode may sag and protrude to the periphery of the metal electrode in some cases.
Additionally, since a cost of Pd (palladium) is approximately 22-fold of that of Ag (silver), and there is a problem that a manufacturing cost rises as an amount of Pd used increases.
Further, in the conventional surface-mounted crystal oscillator, there is a cantilever type that holds a crystal piece at two positions of one narrow side, but there is a region where pulled wiring lines of connection terminals connected to the support electrode at the two positions protrude to the outside of the crystal piece as seen from a top surface of the crystal piece.
Furthermore, in frequency adjustment in a manufacturing process, although an excitation electrode of the crystal piece is scraped away by argon (Ar) ions, but a region protruding to the outside of the crystal piece may be possibly scraped away, and there is a problem that positioning of an ion gun of a regulator is difficult.